Methods for performing major surgery

I need to perform some major surgery on the internals of a Hornby tender so I can fit a large speaker. It's a long time since I have done something like this but my memories are of long and awkward struggles to get a scalpel into just the right place and slowly hacking parts away at great risk to the model and my fingers. There's got to be a better way, so I was wondering what methods people use. I am considering a Dremel fitted with a cutting disc, perhaps running from a flexible shaft.

David